In high temperature environments, it is often necessary to provide electrical connections in or to equipment or instrumentation that must operate in the environment. For example, sensors are often used to monitor the properties of exhaust gas of internal combustion engines where the exhaust temperature can reach 1000° C. Such sensors generally require electrical connections as an integral part of the sensor and/or to connect the sensor to a lead wire for transmission of the sensor output signal. Electrical connection requirements of such sensors can be complicated by the fact that it is often necessary to make the electrical connection to a ceramic element of the sensor.
Mechanical connections are often not sufficiently robust to maintain their performance in the harsh conditions of the high-temperature environment, so wire bonding of a wire to a sensor element is typically employed to provide the electrical connection. Alternatively, brazing techniques may be used to provide the electrical connection. Both of these methods can be expensive and time-consuming to implement.
U.S. Pat. No. 5,730,543 to Schonauer et al. entitled “Electrically Conducting Connection” describes an electrically conductive connection made between a metal connector and a metal layer applied and bonded by sintering to a ceramic substrate comprising glass and/or vitreous ceramic in small quantities. An adhesion-promoting layer having a glass and/or vitreous ceramic and metal particles is applied and bonded by fusion to the ceramic substrate. The metal layer with the sintered bond is then applied to the ceramic substrate and the connector is welded to the metal layer by laser welding.
U.S. Pat. No. 6,437,681 to Wang et al. entitled “Structure and Fabrication Process for an Improved High Temperature Sensor” describes a temperature sensor including an aluminum oxide substrate and a thin-film resistor having a specific temperature coefficient of resistance (TCR) disposed over the substrate. The temperature sensor further includes an aluminum oxide stress-relief layer covering the thin film resistor. The temperature sensor further includes a passivation layer covering the aluminum oxide stress-relief layer. The aluminum oxide stress-relief layer further has at least one resistor-trimming trench formed by removing a portion of the aluminum oxide stress-relief layer and thin-film resistor therefrom and the resistor-trimming trench is filled with a material of the passivation layer. The temperature sensor may further include a set of dummy pads for resistance-trimming measurement disconnected from the thin film resistor disposed on the substrate near the thin film resistor covered by the passivation layer. The temperature sensor may further include a set of sensor bonding pads disposed on the substrate electrically connected to the thin film resistor covered by the passivation layer. The temperature sensor further includes a set of platinum chip-leads bonded to the sensor bonding pads for temperature measurement connections.
The disclosures of the foregoing are incorporated herein by reference in their entireties.
A need remains in the art for a simple, inexpensive, and effective way of establishing electrical connections in harsh environmental conditions.